Precision mold and method of fabrication



March 22, 1966 N. G. LIRONES 3,241,200

PRECISION MOLD AND METHOD OF FABRICATION Filed Sept. 20, 1963 CLUSTERPREt/VET DIP cam DRLl/N sru cc DAY PREIWET DIPIICOAT A /v "N "Times.STUCCO 02w DEI /VAX F/RE METALP OURING l Vacuum INVENTOR. COOL vL Nick6. Zfiones BY mouw REMOVED W,%,@m7a/ZZYW Qz'i 'ys United States Patent3,241,200 PnEcisroN Morn AND METHOD or FABaIcArroN Nick G. Lirones,North Muslregon, Mich, assiguor to This invention relates to the art ofprecision casting and to materials employed in the practice of same andit relates more particularly to a casting process and to compositionsand methods for the preparation of the molds in the practice of same.

It is an object of this invention to produce and to provide a method forproducing new and improved molds for use in the precision casting ofvarious materials and it is a related object to provide a new andimproved molding process employing the same and to provide compositionsfor use in the preparation of same.

More specifically, it is an object of this invention to produce a moldwhich is of sufliciently high strength and stability to enable materialsto be poured directly therein for molding; in which refractory or otherhigh melting point metals can be molded; in which metals can be formedin a manner to minimize oxidation thereby to enable use of the processand materials in the molding of metals that have heretofore beendifficult to shape, and it is a related object to provide a new andimproved molding process which can be easily carried out for theprecision casting of materials which have heretofore not been easilyadaptable to molding and in which the molded products can be easily andefficiently separated from the mold cleanly to release the moldedproduct.

These and other objects and advantages of this invention willhereinafter appear and for purposes of illustration, but not oflimitation, an embodiment of the invention is shown in the accompanyingdrawings in which:

FIG. 1 is a flow diagram of the process embodying the practice of thisinvention; and

FIG. 2 is a schematic sectional view through a pattern having a moldformed therein in accordance with the practice of this invention.

In accordance with the practice of this invention, at least the innerportions and preferably the entire crosssection of a mold is ofgraphitic material formed on the surface of a heat or otherwisedisposable pattern by series of intergrated layers of dip coats andstucco coats but in which the essential solids of the clip coatcomposition and the stucco, including the binder, are all graphitic, as

will hereinafter be described. A mold of such graphite,

material is capable of use at considerably higher temperatures thanceramic materials and many other new and novel characteristics are madeavailable which enable use of the shell for the molding of high alloyand refractory metals.

The new and novel mold will be described with reference to new andimproved compositions employed and the methods of manufacture in arepresentative process illustrating the practice of this phase of theinvention.

In the following description, the terms pattern and cluster will be usedinterchangeably to refer to the wax or plastic pattern 16) or a clusterformed of a multiplicity of such individual patterns. It will beunderstood that changes may be made in the details of formulation,materials and methods employed without departing from the spirit of theinvention.

EXAMPLE 1 Preparation of wax pattern and cluster The pattern 10 isformed of conventional materials disposable by heat or chemicals, as inthe well known investment casting processes. In the illustratedmodification, the pattern is molded under pressure in suitable metalmolds by injection of molten wax to fill the mold and set the pattern.Instead, the pattern can be formed of a thermoplastic, syntheticresinous material or combinations of such plastics and wax.

If the mold is to be formed about more than one pattern, the pluralityof patterns are connected by runners for communication with a pouringspout to form a completed cluster, as described in the Operhall et al.Patent No. 2,961,751. Where, as in the instant process, the cluster isto be repeatedly dipped into a slurry, identified as a dip coat, it isdesirable to provide a hanger rod for carrying the cluster and forsuspending the cluster for drying and the like.

EXAMPLE 2 Dip coat composition 2.77 percent by weight solids ofcolloidal graphite (22% solids in aqueous medium-Aquadag of NationalCarbon Company) 37.8 percent by weight solids of graphite flour (lessthan 200 mesh) 0.174 percent by weight emulsifying agent (gumtragacanth) 0.003 percent by weight anionic wetting agent (sodiumheptadecyl sulphate) Remainder water As the colloidal graphite, it ispreferred to make use of colloidal particles of graphite of less than 1micron. For the purpose of reducing cost, use can be made of acombination of such colloidal graphite mixed with up to 50 percent byweight and preferably up to only 30 percent by weight of semi-colloidalgraphite having a particle size of between 120 microns.

The amount of colloidal graphite in the dip coat composition may varybut it is desirable to make use of an amount greater than 0.5 percent byweight but less than 5 percent by Weight and preferably an amount withinthe range of l to 3.0 percent by weight.

In the dip coat compositions represented by the above formulation, theemulsifying agents and the anionic wetting agents are preferred but notessential. Instead of gum tragacanth, use can be made of otherhydrophilic colloids such as the gums, gelatins, alginates and the like,wherein, when used, such emulsifying agents are employed in an amountwithin the range of 0.01 to 0.5 percent by weight. Instead of the sodiumheptadecyl sulphate wetting agent, other anionic surface active agentsmay be employed such as the allyl sulphates and the allyl arylsulfonates and their salts. When employed, the amount of such surfaceactive agent may range from 0.01 to 0.5 percent by weight of thecomposition.

The dip coat composition will have a pH within the range of 8.8 to 9.4and a viscosity measured by the cup of Patent No. 3,011,986 of between2535 seconds.

The solids content, insofar as the colloidal or semi-colloidal graphiteand graphite flour is concerned, can be varied quite widely, it beingnecessary only to formulate for a viscosity that can be handled to coatthe pattern and to make use of colloidal or semiacolloidal graphite inan amount sufficient to achieve the desired bonding action. For thispurpose, it is deemed sufficient if the latter is present in an amountto make up more than 1.5 percent *by weight of the graphite sol-ids ofthe dip coat composition and it is usually undesirable and uneconomicalto make use of an amount of colloidal or semi-colloidal graphite greaterthan percent by weight of the graphite in the dip coat composition. Itwill be understood, however, that the essentially 100% graphite makingup the solids in the dip coat composition can be achieved by the use ofcolloidal or colloidal and semi-colloidal graphite alone.

Application of dip coat composition The wax pattern or cluster is firstinspected to remove dirt, flakes and other objects which may haveadhered to the surfaces of the wax patterns and which, if allowed toremain, would impair the preparation of a good mold and lead to animperfect casting. The cleaned cluster is immersed into the dip coatcomposition, while being stirred, to cover all of the surfaces of thecluster with the exception of the lip of the pouring spout. To promotethe elimination of air pockets, it is desirable to rotate the clusterwhile immersing in the dip coat composition. Instead of immersing thepattern in the stirred slurry of the dip coat composition for coverageof the surfaces of the pattern, the dip coat composition can be appliedto achieve the desired coverage by spraying the dip coat compositiononto the surfaces of the pattern. By this latter spraying technique thecoating weight of the dip coat composition can be increased ordecreased, as desired, by comparison with the amount of coating retainedon the surfaces by immersion.

When rful'ly coated, the pattern or cluster is suspended to drain excessdip coat composition. During drainage, the cluster can be inspected todetect air pockets which can 'be eliminated by addressing a stream ofair onto the uncoated portions and thereafter allowing the slurry of thedip coat composition to flow onto the uncovered areas. While the clusteris being drained, it should be held in different planes designed toachieve uniform coating on all surfaces. In general, drainage should becompleted within a few minutes but, in any event, in less time thanwould allow the dip coat composition to dry whereby the surface wouldnot retain stucco in the desired uniform arrangement.

EXAMPLE 3 Stuccoing After the cluster has been allowed to drain for ashort time and while the surface is still wet with the dip coatcomposition, the surface is stuccoed with particles of graphite havingthe following particle size distribution.

Tyler screen size: Percent retained on screen 65 62 100 29 150 7 1200 1Pan 1 The graphite will hereinafter be referred to as having a particlesize of more than 150 mesh but less than 35 mesh. The particles ofgraphite are caused to flow over the surface of the pattern until thewet surface is substantially completely covered.

Application of stucco coat 11 tory conveyor. The particles of graphiteadhere to the wet coating and become partially embedded therein tobecome integrated with the coating formed on the wax patterns.

if the dip coat composition is adjusted to enable gallation to [takeplace within a very short period of time, the stuccoed cluster need nothe set aside for drying. However, it is preferred to slow the drying ofthe dip coat so that sufficient leeway is available for the desireddrainage and stucco application. Thus it is desirable to provide for anair dry for a time ranging from 10-25 minutes. It will be understoodthat the drying time may be extended indefinitely beyond the timesdescribed without harm to the structure. If desired, drying of thecombined coatings can be accelerated in a humidity controlled aircirculating chamber heated to a temperature up to about F.

The particle size of the graphite stucco is not critical since theparticle size of the graphite can be varied over a fairly Wide range.However, for best practice of this invention, it is preferred to makeuse of graphite having a particle size greater than mesh and iess than20 mesh.

The operation is repeated, that is the pattern is again dipped into thedip coat composition and covered with fine particles of graphite tobuild up a second composite layer. In the preferred practice of thisinvention, it is desired, though not essential, to precede the immersionof the coated pattern in the dip coat composition with a prewetting stepin which the prewetting composition employs substantially the sameformulation as the dip coat com position with the exception that a lowerviscosity is employed occasioned by the formulation to includeadditional amounts of water suflicient to reduce the total solids toabout 25-75% of the solids in the dip coat composi tion. Thus the coatedpattern is first submerged in the prewe-t composition more completely topenetrate and wet out the coated surface followed almost immediately bysubmersion in the dip coat composition after which the steps ofdrainage, stuccoing with the fine particles of graphite, and drying arecarried out. Thus the layers become better integrated one with the otherto produce a strong and composite structure.

The steps of prewetting, if used, dip coating, stuccoing with the dryparticles of graphite and drying can be repeated several times until amold .112 of the desired thickness and strength has been built up aboutthe disposable pattern or cluster.

While a mold -of higher strength will be secured if the graphiteparticles of the type having a mesh size within the range of more than150 but less than 20 are used throughout to build up the mold, it ispreferred to make use of particles of graphite of larger dimension foruse as the stucco after the second coat and preferably after the fifthcoat. For such outer layers or coatings, graphite having the followingparticle size distribution may be employed.

Tyler screen size: Percent retained on screen 8 1 10 14 20 65 35 18 65 1Pan 1 The foregoing will hereinafter be referred to as having a particlesize greater than 35 mesh but less than 8 mesh.

A mold 12 having a wall thickness of from A to /2 inch is usuallysufficient for the coating of products of normal weight or dimension bymolten metal casting, although molds of greater wall thickness can beformed where greater strengths are desired for use in the molding oflarger castings. The normal wall thickness of mold can be achieved withthe compositions described with from 5-10 cycles of dip coating,stuccoing, and

After the composite mold has been produced, the disposable pattern isremoved to leave a mold cavity in which the material to be molded may becast. Pattern removal, hereinafter referred to as dewaxing, can beachieved in a number of ways:

(a) Use can be made of flash dewaxing wherein the composite is heated toan elevated temperature far above the melting point temperature of thewax or plastic. In a preferred process of flash dewaxing, the compositeis heated to a temperature above 800 F. and preferably to a temperaturewithin the range of 8002200 F. for a time sufficient to eliminate thewax and to fire the mold. When the mold is exposed to a temperature inexcess of 800 F. during dewaxing or firing, it is desirable to enclosethe mold within a reducing or non-oxidizing atmosphere, otherwise thegraphite binder will be burned out.

(b) Dewaxing can be carried out by a process referred to as hot sanddewaxing wherein sand heated to a temperature of 400-800 F. is arrangedto surround the composite for intimate contact with the outer surfacesthereof whereby rapid heat transfer is achieved into the interior tomelt out the wax. The hot sand can be poured about the mold or the moldcan be buried in the hot sand. Instead of sand, use can be made of ametal or alloy system of low melting point such as the cerro alloys, loweutectic alloys, and the like.

(0) Dewaxing can be carried out with steam when the wax patterns areformed of a material having a melting point range below 200 F. For suchpurpose, the composite can be housed within a steam chamber or autoclaveor else steam at relatively high pressure can be addressed onto thecomposite while it is suspended with the spout extending downwardly fordrainage of the molten wax.

(d) Dewaxing can be carried out in an oven heated to a temperature abovethe melting point temperature of the wax but below the oxidizingtemperature of the graphite, or preferably at a temperature within therange of 250-800" F. in a process referred to as low temperaturedewaxing, without the need to maintain a reducing atmosphere.

The mold is thereafter fired by heating to a temperature above 800 F.and preferably to a temperature within the range of 800-2200 F. Firingcan be achieved by exposure of the mold to firing temperature for 15 ormore minutes but it is preferred to fire the mold at a temperaturewithin the range of 8002200 F. for a time within the range of 15-120minutes. Firing can be carried out concurrently with dewaxing when useis made of a high temperature dewaxing method as described in (a) above.Since graphite will be consumed when heated to a temperature above 800F. in an oxidizing atmosphere, high temperature dewaxing and firing arecarried out in an inert atmosphere and preferably in a reducingatmosphere. For this purpose, use can be made of hydrogen or anatmosphere composed of nitrogen or carbon monoxide.

Because of the thinness of the walls of the mold and the high heatconductivity of the graphite, heat penetrates rapidly through the moldto cause the wax portion of the pattern immediately adjacent the innersurfaces of the mold to be reduced to a molten state even before theremainder of the pattern has been heated to elevated temperature. Thusthe liquefied portion leaves sufiicient room to permit expansion of theremainder of the Wax pattern when the cross-section of the pattern isheated to elevated temperature thereby to eliminate strain on the shellwhich might otherwise lead to breakage.

The fired mold is cooled from firing temperature to a safe temperaturebelow 800 F. before exposure to atmospheric conditions for continuedcooling or for further processing.

The fired mold can be used in the as fired state for the conventionalcasting of molten metal.

In the casting of molten materials such as high alloy metals and thelike, it is preferred to densify the interior wall portions of thegraphite mold defining the mold space to minimize flow of moltenmaterial into or through the mold. For this purpose, the mold can beimpregnated with a graphite formulated in an impregnating compositionrepresented by the following:

EXAMPLE 5 lmpregnating composition A 0.5 lbs. colloidal graphite 11.5lbs. acetone lmpregnating composition B i 2 lbs. colloidal graphite (22%solids in aqueous mediumless than 1 micron) 10 lbs. distilled water 25cc. anionic wetting agent For purposes of impregnation, only colloidalgraphite of less than 1 micron should be used. Impregnation can beachieved merely by dipping the fired mold in the impregnatingcomposition whereupon the composition soaks rapidly into the walls ofthe mold. Impregnation is followed by drying. As many as from 1 to 10 ormore impregnations can be effected whereby the pores of the fired moldare increasingly filled with graphite by each impregnation. After one ora series of such impregnations, with intermittent drying, the moldshould again be fired at a temperature within the range of 8002200 F. ina reducing or inert atmosphere for about 15-120 minutes. The resultantproduct, upon cooling, will be found to be of such hardness and densityas to give a metallic ring.

To the present description has been made of the process and compositionswherein a mold formed substantially entirely of graphite is produced.The description will hereafter be made to the use of the new and novelgraphite mold of this invention in the fabrication of shaped products bysuch means as metal casting and vacuum casting of molten metals.

Molten metal can be poured directly into the mold cavity of the graphitemold for the fabrication of molded products of metals of the typegenerally limited to the field of precision casting. The fired graphitemold possesses sufficient strength and has sufiicient mass integrity toenable the molten metal to be poured into the mold without investmentthereby to achieve the many advantages by comparison with investmentcasting such as less weight, less material, more rapid heat-up, morerapid cooling, better control of tear strength, fuller inspection, lowerscrap loss, and the like. The mold can be clamped to the furnace withoutadditional reinforcement or Support When the molten metal is pouredtherein. However, because of the nature of the mold formed of graphite,various modifications are required from conventional molding techniques.

While preheating is not essential, it is desirable to preheat the moldprior to metal pouring. When preheated to a temperature below about 800F. it is not necessary to preheat in a reducing or inert atmosphere, butif the graphite mold is to be preheated to a temperature above 800 F.,it is essential either to preheat under vacuum conditions or in an inertor reducing atmosphere, as in an atmosphere of hydrogen or carbonmonoxide, otherwise graphite will "burn when exposed to oxidizingconditions. Since most precision cast metals have a melting point inexcess of 800 F it is desirable to carry out metal pouring byconventional vacuum casting techniques wherein the graphite mold, withor without preheat, is enclosed Within a vacuum chamber in communicationwith a metal melting furnace whereby a vacuum can be drawn in thechamber in which the mold is mounted to evacuate the chamber prior tometal pouring. The mold and the metal cast therein are preferablymaintained under vacuum until the metal has solidified or the assemblyhas cooled to a temperature below 800 F. Thereafter, the assembly can beremoved from the vacuum chamber for further processing.

An important concept of this invention resides in the ability tofabricate castings of refractory metals and alloys of extremely highmelting point or metals which are subject to rapid oxidation when atelevated temperature, as represented by such metals as zirconium,silicon, tantalum, titanium, and the like. This technicolo-gical advancestems in part from the new and novel characteristics made available froma graphite mold of the type produced by the practice of this inventioncoupled with the means and method by which the molding process iscarried out. Amongst many other desirable characteristics, the graphitemold embodies a desirable degree of porosity; high temperaturestability; high dimensional stability; a desirable balance of highstrength and tear strength, whereby the mold maintains shape duringmetal pouring at high temperature without so much strength as wouldcause tearing of the molded product responsive to differential shrinkageupon cooling; high heat conductivity for rapid cooling or controlledheat transfer for the development of best conditions in the metalpoured; and the ability to maintain an inert or reducing atmosphere forthe protection of the metal while in a molten or highly oxidizablestate, and finally in the ability to effect clean and completeseparation of the mold either by fracture of the graphite mold or byoxidation of the mold to weaken or to burn out the structure.

This phase of the invention will be described with reference to themolding of titanium, it being understood that others of the refractoryor high melting point metals or other metal subject to rapid oxidationat elevated temperatures maybe similarly processed.

While the graphite mold can be used in vacuum molding without processingthe mold to render it inert to reaction with the metal cast, the porousgraphite mold can be so processed to enable metal pouring without vacuumor further to enhance the vacuum molding of molten metals.

In processing to achieve an inert state, the graphite mold is packed ingraphite chips and heated to elevated temperature. A temperature inexcess of 800 P. will be suflicient but it is preferred to heat to atemperature in excess of 1800 F. and more preferably to a temperatureapproaching the temperature of the molten metal, such as within therange of 18002200 F. for 1 to 8 hours. It is desirable to carry out suchheating step in an inert and preferably reducing atmosphere. The heatedmold is evacuated as in a vacuum chamber, to de-gass the walls of themold. The mold is thereafter cooled, preferably to about ambienttemperature, 'while the vacuum is still maintained and thereafter thevacuum is released by bleeding in an inert gas, such as argon, or areducing gas, such as hydrogen, to refill the pores with such inert orreducing gas thereby to purge the mold of oxygen and to block there-entry thereof. De-gassing in the manner described can be repeated oneor more times but such additional purging is not ordinarily required.

The graphite mold, with or without inerting, is transferred to thevacuum pouring furnace and the metal is poured under vacuum into themold, with or without preheating of the mold. When preheating isemployed, it is unnecessary to preheat to a temperature in excess of 800F. although preheating to higher temperatures may be employed.

The firing of the mold and vacuum pouring can be carried out in the samechamber. The graphite mold can be heated in the vacuum furnace to purgethe mold of oxygen and then metal can be poured in the evacuated moldwithout, but preferably after, first refilling the pores with inert gas.

The poured metal is allowed to cool in the vacuum chamber to atemperature below that at which oxidation can take place before removalof the mold for exposure of the poured mold to the atmosphere forfurther cooling.

An important concept of the invention is unique to the type of mold thatis produced. While the cast metal pro duced can be removed byconventional techniques of impacting and shaking to break up the moldand to free the casting and by blasting to remove graphite retained onthe surfaces of the casting, the graphite mold of this invention iscapable of being cleanly and substantially completely removed to leave aclean casting merely by exposure to high temperature in an oxidizingatmosphere, as by heating in air, whereby graphite is consumed. Theentire mold can be caused to be consumed at a temperature above 800 F inan oxidizing atmosphere but it has been found to be sutficient onlypartially to burn out the graphite since the remainder can thereafter beeasily pulled off for clean removal from the casting.

It will be understood that changes may be made in the details ofconstruction, arrangement and operation without departing from thespirit of the invention, especially as defined in the following claims.

I claim:

1. A dip coat composition for use in forming a mold about a disposablepattern for use in precision casting upon removal of the disposablepattern comprising an aqueous composition consisting essentially ofcolloidal graphite of less than 1 micron in diameter, graphite flour ofless than 200 mesh and the balance water, and in which the colloidalgraphite comprises 1.5 to- 10 percent by weight of the graphite solids,

2. A dip coat composition for use in forming a mold about a disposablepattern for use in precision casting upon removal of the disposablepattern comprising an aqueous composition consisting essentially of thecom bination of colloidal graphite and graphite flour and the balancewater, and in which the colloidal graphite is present in the dip coatcomposition in an amount within the range of 0.5 to 5 percent by weight.

3. A dip coat composition for use in forming a mold about a disposablepattern and from which the pattern is removed for use of the mold inprecision casting comprising an aqueous composition consistingessentially of graphite in the form of a graphite flour and graphite inthe form of colloidal graphite with the colloidal graphite comprisingfrom 1.5 to 10 percent by weight of the graphite solids, an emulsifyingagent present in an amount within the range of 0.01 to 0.5 percent byweight of the composition, and the balance water.

4. A dip coat composition as claimed in claim 3 in which the colloidalgraphite component is present in the dip coat composition in an amountwithin the range of 0.5 to 5 percent by weight and in which theemulsifying agent is gum tragacanth.

5. A clip coat composition for use in forming a mold about a disposablepattern and from which the pattern is removed for use of the mold inprecision casting comprising an aqueous composition consistingessentially of graphite in the form of a graphite flour and graphite inthe form of colloidal graphite with the colloidal graphite comprisingfrom 1.5 to 10 percent by weight of the graphite solids, an anionicsurface active agent present in an amount within the range of 0.01 to0.5 percent by weight and the balance water.

6. A mold for precision casting having walls formed in cross-section ofalternate layers wherein one layer consists essentially of a mixture ofcolloidal graphite and graphite flour with the other layer consistingessentially of a graphite stucco and in which the colloidal graphite ispresent in an amount within the range of 1.5 to 10 percent by weight ofthe mixture of colloidal graphite and graphite flour.

7. In the method of producing a mold about a disposable pattern which isremoved to define the mold cavity, the steps of wetting the surface ofthe pattern with an aqueous dip coat composition consisting essentiallyof the combination of graphite flour, colloidal graphite, and Water,with the colloidal graphite being present in an amount within the rangeof 1.5 to 10 percent by weight of the graphite solids, covering thesurface of the pattern while wet with the dip coat composition with agraphite stucco, repeating the cycle of operations a number of timesuntil a mold of the desired wall thickness and strength is built upabout the pattern.

8. In the method of producing a mold about a disposable pattern which isremoved to define the mold cavity, the steps of Wetting the surface ofthe pattern with an aqueous dip coat composition consisting essentiallyof the combination of graphite flour, colloidal graphite and water,covering the surface of the pattern while wet with the dip coatcomposition with a graphite stucco and repeating the cycle of operationsa number of times until a mold of the desired wall thickness andstrength is built up about the pattern and in which the colloidalgraphite is present in the dip coat composition in an amount within therange of 0.5 to percent by weight.

9. In the method of producing a mold about a disposable pattern which isremoved to define the mold cavity, the steps of wetting the surface ofthe pattern with an aqueous dip coat composition consisting essentiallyof the combination of graphite flour, colloidal graphite and water,covering the surface of the pattern while wet with the dip coatcomposition with a graphite stucco, and repeating the cycle ofoperations a number of times until a mold of the desired wall thicknessand strength is built up about the pattern and in which the dip coatcomposition contains an anionic surface active agent present in anamount within the range of 0.01 to 0.5 percent by weight.

10. In the method of producing a mold about a disposable pattern whichis removed to define the mold cavity, the steps of wetting the surfaceof the pattern with an aqueous dip coat composition consistingessentially of the combination of graphite flour, colloidal graphite andwater, covering the surface of the pattern while wet with the dip coatcomposition with a graphite stucco, and repeating the cycle ofoperations a number of times until a mold of the desired wall thicknessand strength is built up about the pattern and in which the dip coatcomposition contains an emulsifying agent present in an amount withinthe range of 0.01 to 0.5 percent by weight.

11. In the method of producing a mold about a disposable pattern whichis removed to define the mold cavity, the steps of wetting the surfaceof the pattern with an aqueous dip coat composition consistingessentially of the combination of graphite flour, colloidal graphite,and

10 Water, covering the surface of the pattern while Wet with the dipcoat composition with a graphite stucco, repeating the application ofthe dip coat composition and stucco for a number of cycles withintermediate drying until a mold of the desired wall thickness andstrength is built up about the pattern, removing the pattern from themold, and firing the mold to a temperature in excess of 800 F. in anon-oxidizing atmosphere.

12. The method as claimed in claim 11 in which the mold is fired to atemperature within the range of 800- 2200 F. in a non-oxidizingatmosphere.

13. The method as claimed in claim 11 which includes the step ofimpregnating the mold after firing by exposing the mold to a solutioncomprising colloidal graphite wherein the graphite has a particle sizeof less than one micron.

14. The method as claimed in claim 13 in which the mold is impregnatedthrough a number of cycles with intermediate drying to produce a moldhaving graphite in high density in cross-section.

15. In the molding of cast shapes with refractory metals comprisingproviding a mold formed of graphite in crosssection comprising layers ofcolloidal graphite and graphite flour alternating with layers ofgraphite, stucco, placing the graphite mold in a vacuum chamber, drawinga vacuum on the mold, reducing the refractory metal to a molten state,introducing the molten refractory metal into the graphite mold whilestill maintaining vacuum conditions, cooling the mold with therefractory metal cast therein to below the solidification temperaturefor the metal before removing the mold from the vacuum chamber, and thenseparating the mold from the cast metal product.

16. The molding process as claimed in claim 15 which includes the stepof burning graphite from the mold for separation of the mold from thecast metal product by exposing the mold to oxidizing conditions while ata temperature above 800' F.

References Cited by the Examiner UNITED STATES PATENTS 2,564,308 8/1951Nagel 106-3828 2,886,869 5/1956 Webb et a1 22-196 2,945,273 7/1960Herzmark et al 22-192 2,948,032 8/1960 Renter 22-193 2,961,751 11/1960Operhall et a1. 22-196 3,005,244 10/1961 Erdle et a1 22-193 3,132,3885/1964 Grant 22-196 MARCUS U. LYONS, Primary Examiner.

3. A DIP COAT COMPOSITION FOR USE IN FORMING A MOLD ABOUT A DISPOSABLEPATTERN AND FROM WHICH THE PATTERN IS REMOVED FOR USE OF THE MOLD INPRECISION CASTING COMPRISING AN AQUEOUS COMPOSITION CONSISTINGESSENTIALLY OF GRAPHITE IN THE FORM OF A GRAPHITE FLOUR AND GRAPHITE INTHE FORM OF COLLOIDAL GRAPHITE WITH THE COLLOIDAL GRAPHITE COMPRISINGFROM 1.5 TO 10 PERCENT BY WEIGHT OF THE GRAPHITE SOLIDS, AN EMULSIFYINGAGENT PRESENT IN AN AMOUNT WITHIN THE RANG OF 0.01 TO 0.5 PERCENT BYWEIGHT OF THE COMPOSITION, AND THE BALANCE WATER.
 7. IN THE METHOD OFPRODUCING A MOLD ABOUT A DISPOSABLE PATTERN WHICH IS REMOVED TO DEFINETHE MOLD CAVITY, THE STEPS OF WETTING THE SURFACE OF THE PATTERN WITH ANAQUEOUS DIP COAT COMPOSITION CONSISTING ESSENTIALLY OF THE COMBINATIONOF GRAPHITE FLOUR, COLLOIDAL GRAPHITE, AND WATER, WITH THE COLLOIDALGRAPHITE BEING PRESENT IN AN AMOUNT WITHIN THE RANGE OF 1.5 TO 10PERCENT BY WEIGHT OF THE GRAPHITE SOLID, COVERING THE SURFACE OF THEPATTERN WHILE WET WITH THE DIP COAT COMPOSITION WITH A GRAPHITE STUCCO,REPEATING THE CYCLE OF OPERATIONS A NUMBER OF TIMES UNITL A MOLD OF THEDESIRED WALL THICKNESS AND STRENGTH IS BUILT UP ABOUT THE PATTERN.